Sintered titanium alloy

ABSTRACT

THE HARDNESS OF SINTERED TITANIUM AND SINTERED TITANIUM ALLOYS IS INCREASED WITHOUT AFFECTING SIGNIFICANTLY THE DENSITY THEREOF BY USING AS THE SINTER POWDER A MIXTURE OF FROM 40% TO 90% BY WEIGHT OF POWDERED TITANIUM OR TITANIUM ALLOY AND FROM 10% TO 60% BY WEIGHT OF A POWDERED HARD SUBSTANCE CONSISTING OF ONE OR MORE OF THE CARBIDES OF THE METALS TITANIUM, CHROMIUM OR VANADIUM.

United States Patent Cflice 3,737,290 Patented June 5, 1973 3,737,290 SINTERED TITANIUM ALLOY Fritz Frehn, Krefeld, Germany, assignor to Deutsche Edelstahlwerke Aktiengesellschaft, Krefeld, Germany No Drawing. Filed Aug. 27, 1971, Ser. No. 175,717 Claims priority, application Germany, Sept. 22, 1970, P 20 46 614.2 Int. Cl. B22f 3/00 US. Cl. 29-182.7 3 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a sintered titanium alloy of high wear resistance and having a hardness exceeding 50 RC.

Pure titanium and titanium alloys are characterised by a particularly favourable ratio of density to strength and by a high resistance to corrosion. In view of these properties titanium and titanium alloys are used for making parts of aircraft and rockets as well as in the construction of chemical plant.

Titanium and titanium alloys are however not very hard and their resistance to wear is poor. The hardness of pure titanium is less than 15 RC and conventional age-hardened titanium alloys have hardnesses between 30 and 40 RC. Wearing parts however are required to have hard nesses exceeding 50 RC, preferably between 60 and 70 RC, and the poor hardness of titanium and titanium alloys has therefore hitherto prevented this metal and its alloys from being used for wearing parts.

It is therefore the object of the present invention to provide a titanium alloy which besides possessing low density and high corrosion resistance and strength of titanium and titanium alloys, also has an improved resisance to wear and a hardness above 50 RC.

The invention provides a sintered titanium alloy consisting essentially of from to 60% by weight of hard substance as hereinafter defined and from 40 to 90% by weight of titanium or a titanium alloy.

By the term consisting essentially of used herein and in the claims hereof is meant that impurities and incidental ingredients may be present in the alloy in small proportions so as not to affect the stated properties.

The hard substance used according to the invention is hereby defined as a carbide of titanium, or a carbide of similar low density and hardness, namely chromium carbide or vanadium carbide, or a mixture of two or more of such carbides. The hard substance consisting of one or more of the said carbides of titanium, chromium and vanadium increases the wear resistance and hardness without adversely aifecting the low density and corrosion resistance of the sintered titanium or titanium alloy.

Due to the high atfinity of titanium for carbon, nitrogen and oxygen, care should be taken when adding the one or more carbides constituting the hard substance to ensure that such hard substance has a very low content of free carbon, free nitrogen or free oxygen to prevent a reaction from occurring during the sintering operation between the hard substance and the titanium or titanium alloy, which by causing changes in volume could lead to porosity of the sintered parts as well as changing the composition of the alloy. It is therefore often desirable to add hard substances having oxygen, carbon or nitrogen contents below the stoichiometric proportion of saturation for such impurities.

The following examples of the invention are provided:

EXAMPLE 1 The hardness of sintered pure titanium of about 15 RC can be raised to between 65 and 70 RC by forming a mixture of titanium and 30% by weight of titanium carbide having a content of free carbon below 0.03%, and sintering the said mixture to obtain a sintered alloy of density 4.57 g./cc.

EXAMPLE 2 An age-hardened titanium alloy consisting essentially of 6.0% aluminium 4.0% vanadium, balance titanium, had a maximum hardness when sintered of 45 RC and a density of 4.43 g./cc.

By adding 25% of titanium carbide before sintering the density of the sintered alloy was slightly increased to 4.50 g./cc., and the hardness was substantially increased to between 60 and 62 RC.

EXAMPLE 3 A titanium alloy consisting essentially of 7.0% aluminium, 4.0% molybdenum, balance titanium when sintered had a maximum hardness of 35 to 40 RC and a density of 4.88 g./cc.

When a mixture of the said titanium alloy with 25% titanium carbide was sintered the hardness was increased to between 60 and 65 RC, the density increasing slightly to 4.60 g./cc.

EXAMPLE 4 A titanium alloy consisting essentially of 5.0% aluminium, 2.5% tin, balance titanium when sintered had a hardness of 25 to 30 RC and a density of 4.46 g./cc.

When a mixture ofthe said titanium alloy and 25% titanium carbide was sintered, the hardness of the sintered alloy was between 57 and 60 RC, the density being 4.47 g./cc.

Thus in each instance the addition of a hard substance according to the invention produced a significant rise in hardness of the sintered alloy often exceeding at the expense of an insignificant increase in density. The hard sintered titanium alloys according to the invention may be used for making parts that are required to have a high resistance to corrosion, particularly to oxidation attack and to media containing chlorine ions as well as being wear resistant and hard. Examples of uses to which the wear-resistant and hard sintered titanium alloys according to the invention may be applied include atomisers, nozzles, stufling boxes, sealing rings, mixer, blades, drain agefittings, stirrers, valves and holders for the chemical, metal, electroplating, paper making, ore dressing, electric, photographic, aircraft and aerospace industries.

The sintering process which may be used for the titanium alloys according to the invention includes grinding a dry mixture of titanium or titanium alloy powder and the pulverulent hard substances as hereinbefore defined in a substantially noninfiammable and non-oxidising liquid to a grain size of less than 5 pm. If the matrix is a titanium alloy the powdered alloy or either of the basic components of the titanium alloy or key alloy may be mixed in powder form and ground with pulverulent hard substance. When alloy components are used, alloy formation between the titanium and the alloying elements takes place during the subsequent sintering operation to form the titanium alloy matrix.

The ground mixture is vacuum dried for the removal of grinding liquid, precautions being taken to avoid selfignition of the finely ground titanium powder, preferably in the mixture, such residuum liquid also provides protection against oxidation and serves as a compacting aid.

The dried mixture is compacted, and the compacted pressing thus obtained are sintered in a vacuum or under a protective gas, preferably in a vacuum higher than 10 torr, at a temperature between 1500 and 1600 C., depending on the particular alloy used.

What is claimed is:

1. A sintered titanium alloy of high wear resistance and of a hardness exceeding 50 RC, consisting essentially of:

4090 percent by Weight of one of titanium and titanium alloy having a hardness no greater than 50 RC; and

10-60 percent by Weight of at least one carbide from the group consisting of titanium carbide, chromium carbide and vanadium carbide.

2. A sintered titanium alloy of high Wear resistance and of a hardness exceeding 50 RC consisting essentially of:

(a) 40-90 percent of one of titanium and a titanium alloy consisting essentially of:

by leaving a residuum of up to 6% of the grinding liquid v ---57 percent by weight of aluminum; and"2.5-4 percent by weight of a metal chosen from the group consisting of tin, molybdenum and vanadium, and balance titanium; and (b) 10-60 percent by-weight of at least one carbide from the group consisting of titanium'e'arbide, chromium carbide and vanadium carbide. 3. The sinterdtitanium alloy of claim ZWherein the carbide is titanium carbide constituting aboutf25 percent 10 by weight of constituents (a) a nd (b). i

References Cited STEPHEN I. LECHERT, JR., Primary Examiner US. Cl. X.R. 

